Thicker planks sound and feel more like real wood.
They don’t have the tapping sound that you get with real thin cheap laminates.

You want to look at other components too, not just the thickness.  You want a minimum of an AC3 wear layer, and I would suggest a AC4.  You also want a core density of 900kg, and a good locking mechanism.
A warranty is always a good sign, but no guarantee as I have heard of many companies not standing behind them, so check out the better business bureau to make sure you are dealing with a reputable company.

If a company won't tell you what components make up their floor, you can rest assure they are low end.  No one pays for high end and then doesn't brag about it.  I think the best 12mm is Old Homestead Floors.

Good luck